POPULATIONS

Definition:All the members of a species that live in one place at one time.

PROPERTIES of Populations

Geographic dispersion—the way in which individuals of a population are spread in an area or volume.

Eg. Bears, owls, tigers

Eg. Dandelions Eg. Wolves, bison, elephants

Population Growth SIZE

Definition Population SIZE

The number of individuals in a population

Population Growth RATERATE

Depends on: Birth Death Emigration: movement of individuals OUT OF a

population Immigration: movement of individuals INTO a

population

+-

-

+

Population Size Calculation

What if there were1267 rabbits in a colony. In one year 1500 rabbits were born, 1285 died, 65 emigrated and 0 immigrated. What is the new size of the population?

Answer: 1417 What would the number look like if

there was a decline in population growth?

Negative number

Population Growth RATE

Population growth RATE The amount by which a population’s size changes

over time.

2 Types of Population Growth Rate

1. Exponential2. Logistic

EXPONENTIAL Model of Population Growth A population grows exponentially when resources are

abundant. If a population grows exponentially the population size

increases dramatically over a period of time.

Do the Math

Fill in the chart with the correct quantities

Time (minutes)

Formula Number of Cells

0 20  020 21  240 22  460 23  880 24  16100 25  32120 26  64140 27  128160 28  256180 29  512200 210  1024

Positive Feedback

Exponential growth is an example of positive feedback. The more

organisms there are, the more babies will be born who, in turn, grow up to have babies themselves and so on.

Positive Feedback

Positive feedbacks can be expressed in graph form as well.

“J” shaped curve

Exponential Growth Curve

Trace the trend line for the exponential growth curve and

label the x and y axes with appropriate terms and

Add a title

Time vs. Number of Individuals

LogisticModel of Population Growth

Most populations face limiting factors and thus show a logistic growth rate.

Populations are limited by finite resources in the environment.

Logistic Population Growth

The amount of resources in an environment dictates its carrying capacity.

Definition:

The number of individuals

the environment can support

over a long period of time

Negative Feedback

Logistic growth is an example of negative feedback.

Since resources are limited, there is competition for these resources, therefore death rates rise, causing the population to stabilize.

Negative Feedback

Examples of abiotic limiting factors temperature Space

Examples of biotic limiting factors Food comepetition

Logistic Growth Curve

On your notes trace the trend line Label the x and y axis Add a title Label the phrases

Birth rate increases Death rate increases Carrying capacity

LOGISTIC Model of Population Growth

Negative Feedback Loops can be expressed in graph form

Stretched out “S”When population is small,

birth rate is higher

than death rate

As population reaches

carrying capacity,

death rate increases

When at carrying capacity,

birth rate is equal to

death rate

Logistic Growth Curve

Often the population oscillates up and down, but there is an overall equilibrium to the population.

Draw in the carrying capacity line in your notes

Carrying Capacity

Logistic Growth Curve

The carrying capacity is around 1.5 million individuals

Population DENSITYNumber of individuals per unit of

area

Population DENSITY

Definition:

Low densityHigh density

Do the math

In a 3 km 2 area there are 7 deer. What is the density of the deer population? Answer: 0.42deer/km2

Population Size REGULATION

1. Density Independent Factors: reduce population regardlessregardless of population sizeExamples: Weather Fires Floods

Population Size REGULATION

2. Density Dependent Factors: triggered by increasing population densityExamples Food shortages Space limitations Waste accumulation